Electrolytic condenser



April 3, 1951 J. B. BRENNAN 2,547,371

ELECTROLYTIC CONDENSER Filed Sept. 18, 1947 2 Sheets-Sheet 1 IN V ENTOR. L70 SEP/7 B-BEEA/A/A/V' April 3, 1951 J. B. BRENNAN 2,547,371

ELEcTRoLYTIc coNnENsER Filed sept. 1s, 1947 2 sheets-sheet 2 INI/EN TOR.TOSEPH BBEE/V/V/4/V BYM W l A 7 TO/VEYS Patented Apr. 3, 19f51nLncrnonY-'rio coNnsN-sna Joseph-B;-

Application september 1s, r947v,lsria1= No. 774,829

This invention relates to` electrolytic condensers `of the type'embodying electrodes oispra'y deposited metal, and the presentapplication constitutes a continuation in part oirny copendingapplication Serial No. 591,909, filed May 4, 1945, and of my Vcopendingapplication` lSerial ',No. 419,157, filed November 14, 1941, now PatentNo.. 2,446,524, which in turn is a continuation in part off `my'application Serial No. l58,l05-led August 9, 1937, now Patent No.2,280,789, issued April 28, 1942.

In my prior applications aforesaid, I disclosed electrolytic condensersembodying electrodes composed of porous layers of spray depositedmaterial on flexible porous base 'materials such as woven gauze,aluminum screen,` lter paper and glass cloth. The present applicationrelates to condensers in which the layers making up the electrodescomprise' minute cohering particles of metal deposited upon very thin,soft/and porous paper strips and in which the vspacers lare composed ofsimilar thin and porous'paper. vBysuch a construction, condensers which'are porous substantially throughout are obtained; such condensers, inaddition to having very high capacity per unit Vof volume, which resultsfrom the nature of .the electrode surfaces andthe thinnessof theelectrode strips, also have other advantageous characteristics whichhave not .heretofore been possible'of attainment. 'i 'f Thus, condenserassemblies made according to my invention are .of'such a porous 'naturethat the impregnation ofthe assemblies'with elec trolyte can be carriedout'rapidly merely by immersing the assemblies' in electrolyte, allofthe components of the condenser assemblies being of such a capillarynature that the electrolyte'is drawn into the assemblies in a iewminutes. lur-4 thermore, the condensers have lower power factor than anyprior condensers of' which jvam aware. Eiciency of operation is alsomaintained under a wide range iof temperatures; condensers madeaccording to my invention lose 'less than of their capacity uponreductionin temperature from 70 F. to '-13" F. as distinguished romtheloss of A% or more in priortypes vof condensers utilizing the sameYelectrolyte. My condensers also have the Vvery desirable chanacteristicof withstanding .overloadsand surges .of current far better than anypriorn types cof velectrolytic condenSSrS. For reasons of WhichI am notentirely aware, condensers made according to my ini/entiendo notibeeomeshort vcircuited when ,subjectto large overloads yand' under Atheiniruence-,of a ,large overload uor aishort 'period 3 Claims (Cl-'lilt nof time, the condensers merely Pass a greater amount: offleakagecurrent, and upon reduction of theV voltagey t0 liQrmal value, normaloperation of thev condenser-s is regained very promptly. Ithe'overloadisimposed for a long enough Yperiool '0iy vtiine'to evaporate substantialquantities Y0imoisturel from the electrolyte, the condenser does notflash or become short circuited, but' acsaires the characteristes Of atesis???- Even though thecondenser may be subjected 'to Such a-prolongedoverload as'to substantially destroy its Qreability as a. eenldenser,nevertheless -it still will function to prevent the passage of largeamounts of current, and thus it is unlikely f that failure of one of mycondensers under over# i gpge, and if the voltage is imposed 'for' alonger 'period of time and the electrolyte destroyed by evaporation ofthe liquidtherefrom, then thecondenser acts in the manner of 'aresistor'. Lower veltage condensers such as those designed for operationat yI volts lhave an ability to withstand surges ofthe order of 200volts without substantial damage, andif the overload is Icontinued,'thecondensers will frequently form additional Adielectric film thicknessand operate at the higher voltage without undue leakage.

Apreferred form of condenser for giving the aforesaid Iadvantageusresults is illustrated in the drawing in which Figure l Sher/Svar115112.01# typercondenser embodying my invention with the electrodespartially unrolled in order to show the construction of the condenser;Figure y.2 'is across section through the condenser shown in Figure lwith .the elements separated somewhat for convenience of illustration;Figure 3 Vis a greatly enlargedY crossfsect-ional View oi a small pieceo ian electrode-made according to my invention; and Figure4diagrammaticallyillustrates an apparatus forproducing my electrodes.The drawing is vnecessarily somewhat diagrammatic andV no effort hasbeen made' to draw the parts toscale. Asshown 'in-.the drawing, acondenser embodying myfinvention and' adapted for direct current.service may `comprise 'an anode il! having a" 'terminal' 1Hsecuredtheretof"spacer@l2,1 a cathode havingfsafterminal' l5 securedthere-to Y `edges throughout their lengths.

and another spacer I6. All of these elements may be enrolled intosubstantially cylindrical form as indicated at I1, and the 'enrolledcondenser may be enclosed in -a suitable can or casing (not shown) fromwhich the terminals project. The general configuration of the condensermay be conventional and may be varied to suit different requirements.Also, it will be understood that more than two electrodes or plates maybe p-rovided vand that my condensers may be adapted to alternatingcurrent services if desired.

In order to obtain the desired porosity of the condenser, the conductivelayers of the anode and cathode are deposited upon paper strips, and thespacers l2 and I6 comprise paper strips. Preferably the paper in eachcase is a porous, soft paper such as a lightly calendered kraft paper.The paper` should be free from chlorides and sulfates and otherimpurities which would contaminate the condenser; the paper sold in thetrade as electrolytic condenser kraft paper is well suited to mypurposes. The spacers l2 and l5 are composed of paper preferably from0.002 to 0.004 inch thick (electrolytic condenser kraft paper issuitable), although the thickness of the spacers is not critical so longas they are thick enough properly to separate the electrodes or platesl0 and i4 .and are not so thick that they add undue bulk to thecondenser assembly. It will be noted'that, as shown in Figure 2, thespacers are slightly wider than the anode l0 and cathode I4 to preventcontact between the edges of these electrodes.

In making the anode I0, the paper strip on which the conductive metallayers 2l and 22 are deposited preferably has a thickness of only 0.001inch, and it is possible to employ papers as thin as 0.0005 inch as thebase. The thickness, however, preferably should not exceed 0.0003 inch,as additional thickness merely adds bulk to the condenser and decreasesthe flexibility of the electrode without any corresponding advantage. Oneach side of the strip there are porous, flexible conductive layers 2land 22 composed of nely 1 divided particles of `film-forming materialwhich cohere to each other and adhere firmly to the baseV strip. Theselayers must be thick enough to be conductive and thin enough to bereadily flexible. of about 0.0025 inch are very satisfactory, and Iprefer that the thickness of each layer be not more than 0.003 inch. Thetotal thickness of the anode preferably does not exceed 0.007 inch. Thelayers should be of substantially uniform thickness throughout, and thelayers extend around the edges of the paper base as indicated at 23 and24; thus, the conductive layers are in electrical contact with eachother along their Preferably the layers are produced by sprayin iinelydivided molten particles of film-forming material such as aluminum of99.8% purityor better upon the paper strip by moving the paper strippast the nozzle of the spraying apparatus at a speed which is correlatedwith the rate of spraying so that a single pass of the strip past thespraying nozzle produces a deposit of the desired thickness. Thespraying operation is carried out first on one side of the strip andthen on the other, and the spray nozzle is adjusted to produce a sprayslightly wider than the strip so that the edges are covered as indicateddiagrammatically in the drawing. The strip is moved at auniform velocitypast the spray nozzle, and

I have found that layers on each side f 4, the molten metal isdischarged at a uniform rate* from the spray nozzle, the velocity of thestrip and the rate of discharge being correlated tov give the desiredthickness of, for example, 0.0025 inch on each side.

The operation is carried out continuously and rapidly, preferably at aspeed of about 15 feet perr minute. After the spraying operation iscompleted, the anode is formed in strip form by' passing it continuouslythrough a bath contain-A ing a film-forming electrolyte at atemperature: of approximately C. and by passing a unidirectional currentthrough the strip.

1f the spraying is carried out by an apparatus such as a Schoopmetallizing gun, the gun is positioned far enough away from the paper sothat the paper is not carbonized by the flame. For example, I haveobtained good results by spraying on a strip moving at the speed of 15feet per minute with a metallizingy gun sup ported 81A? inchesfrom thestrip, using 1A; inch aluminum wire of 99.8% purity, fed at a speed of40inches per minute, using an oxygen pressure of 40 lbs. per square inchand propane pressure of 40 lbs. per square inch in the gun, andemploying compressed `air under a pressure of 60 lbs. per square inch toatomize the molten aluminum and project the particles against the strip.By spraying layers about 0.0025 inch in thickness on both sides ofthestrip in the manner noted above, I obtain porous, flexible anodes whichhave a capacity per unit of area of from eight to ten times the capacityof an electrode of plane high-purity aluminum foil would have under thesame test conditions.

It is to be noted that the soft, porous paper on which the metal isdeposited has very little strength when wet, and in fact willdisintegrate when subjected to handling in the formation electrolyte at90 C. Thus, the strip itself does not have anything like the strengthrequired to permit it to be drawn through the formation bath over theseveral guide rollers necessary to guide the strip through the bath.However, the spraying operation carried out as described above causesthe molten or plastic particles of aluminum to impinge upon the paperwith suficient'force that the particles are flattened slightly as vtheystrike andl many of them are embedded in the paper and become rmlybonded to the underlying paper fibers. Then as the spraying operation iscarried out progressively with the paper moving past the spray nozzle,succeeding particles are deposited upon the previously depositedparticles before the previously deposited particles are ccmpletelychilled, somewhat in shingle or fish-scale fashion, although the layersare several particles thick, producing in a single pass through thespray a structure in which particles are bonded to adjacent particlesand are also bonded to underlying paper fibers. c

Figure diagrammatically illustrates the nature of the resultantmaterial. Here the paper fibers are indicated at 20a, the aluminumparticles making up the layer 2l are indicated at 2la, and the aluminumparticles making up the opposite layer 22 are indicated at 22a.Particles in each layer are bonded together with interstices, passagesand the like between the unbonded portions of the particles. It will benoted that some .of the particles Zla penetrate substantially throughthe strip and are embedded within the iibrous structure of the paperstrip, some of the particles being locked to two or more fibers.VSimilarly some of the particles 22a penetrate into the Vstrip and areembedded therein. Thus, some of the particles 22a. are bonded throughthe paper strip to some of the particles 2|a. The penetration of thealuminum particles into the paper strip is such that after the paperstrip has been sprayed on one side, it is possible to see aluminumparticles through the paper from the unsprayed side; when the votherside is sprayed, it is these penetrating particles of each layer thatare bonded to each other. This bonding through the strip not onlyfurther reinforces the paper layer, but also serves to retain theparticles on the layer and to provide many conductive paths for thepassage or" electricity between-the layers on opposite sides of thepaper strip, these paths being in addition to the paths provided by thecontact between the layers around the edges of the strip as at 23 and24.

Thev penetration of the particles into the paper strip is such that thespacing between the two deposited layers is less than the originalthickness of the paper. For example, I have found that if electrolyticcondenser kraft paper having a thickness of 0.002 inch is sprayed with alayer in the manner described above such that the total thickness of thepaper and the sprayed layer is 0.004 inch, and the paper then burned outor otherwise removed, the average thickness of the sprayed layer isapproximately 0.003 inch, indicating a penetration of the layer into thepaper of about ;()0'1 inch, although, as noted above, some of theparticles of the layer penetrate farther than this and some penetratelesser distances or not at all.

The bonding of the particles to each other and to the paper bers resultsin a reinforcement of the paper by the spray deposited layers. The bondsbetween the paper bers and the metal particles and the bonds between themetal particles do not seem to be substantially affected by the hotforming electrolyte, and thus the soft paper, which may be of low wetstrength, is given sucient additional wet strength by the sprayingoperation to permit it to be lhandled in the usual manner in formationwithout requiring any special precautions and without danger of tearingor breaking. -This reinforcement of the strip by the adherent coatingsmakes it possible to use porous, soft paper which the electrolytereadily penetrates and to which the deposited coating rmly adheres.

The paper preferably is of such thinness and softness that when thefinished electrode is immersed in hot electrolyte, the paper will notswell enough to blister or crack the deposited metal. The porous softpaper after spraying is given greater strength by the embedded andbonded spray deposited particles than a hard calendered paper of thesame composition and weight would have after spraying because theparticles do not penetrate and adhere as well to the hard calenderedpaper. Thus, by using a softer, weaker paper to start with, Iunexpectedly obtain an electrode that is stronger and more flexible whenwet with a hot electrolyte than can be obtained by spraying layers ofthe same weight on a harder, stronger paper of the same generalcomposition and thickness. Therefore, I am able to use a soft paper withlow wet strength, a1- though it is to be understood that papers of highWet strength may be employed so long as they are sufficiently soft andporous to admit of proper bonding with the spray deposited metal;

lThe deposited layers, produced in the manner described, are alsouniformly highly conductive.

Thus, anl ar-iode"` stri-'p 2% inclv wide hav-ing twd sprayed layersapproximately 0.0025- inch in thickness has a conductivity such that aformation current of from 40 to 50 amperes at 550 volts may be appliedto it without overheating the strip. The conductivityl is suiiicientlyunifform that no localized spots of high resistance which would besubject to overheating are present, and the character of the depositedmaterial is of such uniformity that the capacity per unit of area Variesless than from point to point lengthwise of the strip.

In Figure 4 of the drawing, I have diagrammatically illustrated anapparatus suitable for carrying out the spraying process just described.As shown in this figure, the strip 2c is fed from. a supply spoolthrough a pair of rolls 26 and. around the roll 2 which furnishes abacking for the strip while the spray from the sprayl gun 28 is directedthereagainst.- The strip then. passes around the guide roll 29 and thebacking roll-30 Where the other sideof the strip is sprayed by means ofthe gun 3l. Preferably the backing rolls 2l and 30 are cooled by wateror other suitable fluid during the spraying operation, and while thesprayed particles penetrate the soft porous paper as described above,nevertheless` the paper does not permit any substantial nurnber ofparticles to pass through it and impinge upon the backing rolls. Thespraying operation, therefore, does not have any substantial tendency tobond the paper to the backing rolls.

The guide roll 32 leads the strip to the pinch rolls 33 where anelectrical connection is made between the metal coatings on both sidesof the strip and the positive terminal of the direct current generator34 which furnishes the formation voltage. From the rolls 33 the strip isguided in a multiplicity of passes by guide rolls 35 immersed in theformation electrolyte 3S in the tank 3l, the tank 31 and copperelectrodes 31a being connected tothe negative terminal of the generator34. The strip is drawn through the formation tank by the driven pinchrolls'38, and the sprayed and formed strip may then either be severedinto appropriate lengths for electrodes or may be wound onto a take-upreel 39 as shown.

If desired, the sprayed strip may be subjected to a rolling operation bypressure rolls 4| to flatten and smooth the spray deposited layersand/or may be heat treated to anneal the particles. It is alsocontemplated that the spraying operation may be carried out in anon-oxidizing atmosphere if desired.

The electrodes are completed by cutting the strip into proper lengths,the length beingT determined by the amount of capacity desired in thecondenser to be produced, and by securing a ter-V minal Il to eachelectrode. The terminal Il is preferably composedgcf the samenlm-forming metal as is used in the spraying operation, thus, in theexample given, the terminal preferably is composed of high purityaluminum foil of about 0.005 inch in thickness. The terminal is stakedto the electrodev by punching out triangular tongues in the terminal asindicated at 40, the tongues extending through both sprayed layers andthe paper as shown invFigure 2, thus making good contact between theboth sprayed layers.

The cathode ld may be made in substantially the same manner as theanodev I 0, but preferably, for economy ofmaterialY and to save space,the paper` strip 42 'of the cathode is provided with a sprayed layer 43on onlyrone side thereof. The

terminal and paper strip preferablyis identical with the strip used inthe manufacture of the anode l0, but

the spray deposited layer 43 may be slightlyl on the cathode being from0.0025 inch to 0.004k

inch, and the total thickness of the cathode preferably being notgreater than 0.005 inch. Herel again, the sprayed layer reinforces thepaper and gives itincreased wet strength, which may be of importance ifthe cathode is Wound into the condenser while wet.

In constructing the cathode, I preferably use the same aluminum, thatis, aluminum of 99.8% purity or better, as was used in making the anode.While such aluminum is more expensive than ordinary commercial aluminum,there is such a small amount of aluminum used in the cathode that theadded cost per condenser is practically negligible. It is advantageousto use the same metal for both anode and cathode as it eliminates theneed for having two different ried out by spraying on one side of thestrip in a continuous manner as described in connection with the anode.Thereafter, the cathode strip is severed into appropriate lengths, thecathode in a given condenser being of approximately the same length asthe condenser anode. A terminal member I5 is attached to each length inthe same manner as terminal ll is attached to the anode. The assemblymay be made by rolling up an anode, a cathode and separators intocylindrical form as shown; the assembly is then immersed in the finalcondenser electrolyte which may consist of a conventional boricacid-glycol electrolyte, which is viscous or pastey at ordinary roomtemperatures and which may be heated to increase its fluidity,rfor aperiod of l or l minutes in which time it will have absorbed bycapillary action enough electrolyte to completely saturate the assembly.The condenser'is then aged kby applying current to it in order to form adielectric lm on the cut ends of the anode and on unformed portionsof-lthe anode terminal, this operation requiring only a few minutes.Then the assembly is removed from the electrolyte and placed in aconventional can or other container. The capillary attraction of theassembly for the electrolyte is such that sufficient electrolyte for theoperation of the condenser is retained inv the assembly as it is removedfrom the aging bath, and it is unnecessary to add any additionalelectrolyte after the assembl'y has been placed in the final container.While I have described my Vcondenser as embodying pastey or viscouselectrolytes, it is to be understood that more liquid electrolytes, aswell as electrolytes that are solid at room temperam tures may beemployed; the solid electrolytes are liquined by heat to impregnate thecondensers.

As noted above, condensers made according to my invention giveremarkably good results. While all of the reasons for their advantageousoperation are not entirely understood by me, it

seems probable that at least some of the advanor the like.

tages' flow from the fact that the spraying operation produces a finelyroughened, yet uniforml surface Von the electrodes, the spray depositedYlayers are of substantially uniform thickness throughout and are ofuniform conductivity throughout. Thus, the current density throughoutthe condenser is substantially uniform. The surfaces of both the paperseparators and the sprayed electrodes are also generally fiat; that is,there are no pockets or substantial variations in thickness such asoccur with electrodes in which spray deposited layers are deposited onvbases composed of woven cloth such as gauze Furthermore, thepermeability of the electrode and of the separators is substantiallyuniform throughout. Thus, there are no pockets where there can beaccumulations of gas; any gases generated in the operation of thecondenser can nd their way out of the assembly readily throughrelatively short paths because of the permeability of the entireassembly.

The porosity of the spray deposited material and the capillary nature ofthe electrodes and spacers is such that the wound condenser assemblyacts like a blotter or sponge in absorbing electrolyte. The porosity ofthe assembly extends in radial as Well as axial directions, and becauseof the porosity in all directions, the internal resistance of theassembly to the passage of ions and gases within the condenser is lessthan in previoustypes of condensers, resulting in condensers which aremore efficient from an electrical standpoint and in which generation ofgas has substantially no damaging effect.

The uniformity in thickness and in other characteristics means that eachpart of the condenser is subjected to substantially the same electricalload as every other part. This uniformity prefvents overloading oflocalized areas in the con? denser and eliminates hot spots andlikelihood of local failure. y

.Those skilled in the art various modifications and changes can be madein my invention without departing from the spirit and scope thereof. Itis therefore to be understood that my patent is not limited to thepreferred form of the invention described herein or in any manner otherthan by the scope of the appended claims.

I claim: l

1. An electrolytic condenser assembly comprising at least two flexibleelectrodes and intere leaved spacers, each electrode comprising a sheet.of soft, porous paper having a thickness of less than 0.003 inch and aporous conductive layer of finely Ydivided. metal particles coating thesame, one of said electrodes constituting an anode a and having layersof metal particles coating both sides thereof, the finely divided metalparticles l on the side of each layer engaging the paper sheet beingembedded in the porous paper sheet and embracing and bonded to thefibers of the paper forming the sheet, some of the innermost 1 embeddedparticles of metal of a layer projecting through the strip to theopposite side of the strip, all the particles of metal of one layerbeing bcnd ed together, and some of the particles of metal of 1 onelayer of the sheet of paper coated on both sides being bonded to some ofthey particles of metal of the other layer, said metal coated papersheets being reinforced and strengthened by the coatings of bonded metalparticles and being capable of flexing without separation of thecoatings from the sheets, said metal particles being will appreciatethat electric lms formed thereon, the spaces each comprising a sheet ofporous paper, the entire assembly being porous and evidencingcapillarity substantially throughout and being impregnated with aviscous, nlm-maintaining electrolyte.

2. An electrode for electrolytic condensers comprising a strip ofporous, soft paper having a thickness of less than 0.003 inch, and aporous conductive layer of nely divided particles of high purityaluminum coating each side thereof, the nely divided particles ofaluminum on the side of eachlayer engaging the paper strip beingembedded in the porous paper strip and embracing and bonded to thefibers of the paper forming the strip, some of the innermost embeddedparticles of aluminum of one layer projecting through the strip to theopposite side of the strip, all of the particles of aluminum of onelayer being bonded together and some of the particles of aluminum of onelayer being bonded to some of the particles of aluminum of the otherlayer, thereby forming an aluminum coated paper strip reinforced andstrengthened by the coating of bonded aluminum particles and capable offlexing Without separation of the coating from the strip.

3. An electrode for electrolytic condensers comprising a strip ofporous, soft paper having a thickness of less than 0.003 inch, andaporous conductive layer of finely divided particles of high purityaluminum coating one side thereof, the nely divided particles on theside of the layer engaging the porous paper strip being embedded in theporous paper strip and embracing and bonded to bers of the paper formingthe strip, some of the innermost embedded particles of aluminumprojecting through the strip to the opposite side thereof, all of saidparticles being bonded together thereby forming an aluminum coated paperstrip reinforced and strengthened by the coating of bonded aluminumparticles and `capable of fiexing Without separation of the coating fromthe strip.

JOSEPH B. BRENNAN.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS y Date Number Name 2,177,819 Booe Oct. 31, 19392,280,739 Brennan Apr. 28, 1942 2,290,338 Kcehring July 21, 19422,295,759 Scheer Sept. 15, 1942 2,297,607 Blackburn Sept. 29, 19422,310,932 Brennan Feb. 16, 1943 2,375,211 Brennan May 8, 1945 2,384,500Stall Sept. 11, 1945 2,404,824 Booe July 30, 1946 2,412,201 Brennan Dec.10, 1946 FOREIGN PATENTS Number Country Date 543,505 Great Britain Feb.27, 1942

